The present invention relates to a method of and apparatus for controlling the idling speed of an internal combustion engine.
An idling speed control device has been known in which a bypass passage branches off from the main intake passage of an engine, upstream of a throttle valve, and connects again to the main intake passage downstream of the throttle valve. A diaphragm type vacuum operated control valve device is arranged in the bypass passage. The diaphragm vacuum chamber of the control valve device is connected via a vacuum conduit to the intake passage located downstream of the throttle valve, and an electromagnetic control valve is arranged in the vacuum conduit for controlling the cross-sectional area of the vacuum conduit. In this idling speed control device, during idling, the level of the vacuum produced in the diaphragm vacuum chamber of the control valve device is controlled by adjusting the electromagnetic control valve in accordance with the operating condition of the engine. In addition, the air flow area of the bypass passage is controlled in accordance with a change in the level of the vacuum produced in the diaphragm vacuum chamber. As a result, the amount of air fed into the cylinders of the engine from the bypass passage is controlled. However, in such a conventional idling speed control device, firstly, in the case wherein a vehicle is used in a cold region, the electromagnetic control valve becomes frozen and, thus, it is impossible to control the cross-sectional area of the vacuum conduit. As a result, since it is also impossible to control the air flow area of the bypass passage, a problem occurs in that it is impossible to control the amount of air fed into the cylinders from the bypass passage. Secondly, in a conventional idling speed control device, since the diaphragm type vacuum operated control valve device is used, the controllable range of the air flow area of the bypass passage is very narrow. Therefore, even if the control valve device is fully opened, the amount of air necessary to operate the engine during fast idling, cannot be fed into the cylinders of the engine from the bypass passage. Consequently, in a conventional idling speed control device, an additional bypass passage is provided in addition to the regular bypass passage, and a valve, which is actuated by a bimetallic element, is arranged in the additional bypass passage. When the temperature of the engine is low, the valve, which is actuated by the bimetallic element, opens. As a result, since air is fed into the cylinders of the engine from the additional bypass passage in addition to the air fed into the cylinders of the engine from the regular bypass passage, the engine receives the amount of air necessary for fast idling. As mentioned above, in a conventional idling speed control device, since the additional bypass passage and the valve, actuated by the bimetallic element, are necessary in addition to the regular bypass passage, a problem occurs in that the construction of the idling speed control device will be complicated. In addition, since the amount of air fed into the cylinders of the engine is controlled by only the expanding and shrinking action of the bimetallic element during fast idling, it is impossible to precisely control the amount of air fed into the cylinders of the engine.